1. Field of the Invention
This invention relates to a lubricant composition and is particularly concerned with a transmission lubricant suitable, for example, for helicopter transmission systems.
2. Description of Related Art
The development of new transmission systems, for example, for helicopters, has led to the requirement for dedicated lubricants for such purposes which can meet demanding load carrying and corrosion protection criteria. Specifications put forward by, for example, the U.K. Ministry of Defence and the United States Navy, pose requirements to be met by new dedicated helicopter transmission lubricants that cannot be fulfilled by existing aviation turbine engine lubricants. There is thus a need for the development of new and improved lubricant compositions for such purposes. The present invention seeks to fulfil this need.
DE-A-2039785 discloses a load carrying additive composition for a gas turbine engine. The load carrying additive composition comprises a synthetic ester base stock fluid having a viscosity of 5.6 to 6.0 cs. at 99.degree. C. (210.degree. F.) (see the examples).
U.S. Pat. No. 3,694,382 discloses a lubricant for a gas turbine engine. The lubricant comprises a synthetic ester base stock having a viscosity ranging from 4.0 to 9.1 cs. at 99.degree. C. (210.degree. F.).
FR-A-2215462 discloses a lubricant having a mineral oil as its base stock.
WO-A-9410270 discloses a corrosion inhibiting lubricating composition comprising a synthetic base stock having a viscosity of at least 4.9 cSt at 100.degree. C.